TinyMCE not saving content

I have built a Perch site that uses TinyMCE as its content editor (against my advice... grrrr)

One particular template uses blocks and on some pages (when there are two instances of TinyMCE) the content in the second instance does not update. This only occurs in Firefox. It seems to work fine in Chrome.

Blocks template:

<perch:blocks>
    <perch:block type="twocol" label="Two col">
        <perch:template path="content/blocks/2col.html" />
    </perch:block>
    <perch:block type="text" label="Just text">
        <perch:template path="content/blocks/justtext.html" />
    </perch:block>
    <perch:block type="image" label="Just image">
        <perch:template path="content/blocks/image_block.html" />
    </perch:block>
    <perch:block type="image_text" label="Image Text">
        <perch:template path="content/blocks/image_text.html" />
    </perch:block>
    <perch:block type="image_grid" label="Image Grid">
        <perch:template path="content/blocks/image_grid.html" />
    </perch:block>
    <perch:block type="sectors" label="Sectors">
        <perch:template path="content/blocks/sectors.html" />
    </perch:block>
    <perch:block type="map" label="Map">
        <perch:template path="content/blocks/map.html" />
    </perch:block>
</perch:blocks>

Typical block that displays this issue

<div class="row">
    <div class="col-sm-12">
        <perch:content id="leftcol" type="textarea" label="Content" html="true" editor="tinymce" imagewidth="640" imageheight="480" />
    </div>
</div>

Additionally (may be related), If you drag a block with TinyMCE inside to reorder, the content disappears completely - seems to be the issue mentioned at https://forum.grabaperch.com/forum/07-02-2015-disappearing-block-content and https://forum.grabaperch.com/forum/07-25-2016-tinymce-editor-removing-block-content-when-re-ordering-items if that is of any help.

I never have of these problems using MarkItUp (which is what I use and recommended...again...grrrr)

Many Thanks

Diagnostics

Perch Runway: 2.8.32, PHP: 7.0.1, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: 7e72f9690b1498a1bead7a637c33a831c0d2f655 $, with PDO
Server OS: Linux, cgi-fcgi
Installed apps: content (2.8.32), assets (2.8.32), categories (2.8.32), perch_blog (5.0), perch_forms (1.8.3), perch_shop_orders (1.0.9), collection_1 (2.8.32), perch_shop_products (1.0.9), perch_shop (1.0.9), perch_members (1.5), perch_twitter (3.6.2)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_blog', 'perch_forms', 'perch_members', 'perch_shop', 'perch_twitter' );
PERCH_RESFILEPATH: /.../public_html/assets/resources
PERCH_LOGINPATH: /perch
PERCH_PATH: /.../public_html/perch
PERCH_CORE: /.../public_html/perch/core
Image manipulation: GD
PHP limits: Max upload 100M, Max POST 100M, Memory: 128M, Total max file upload: 100M
F1: 2edba60ed1f613d6dd804feb202456a2
Resource folder writeable: Yes
DOCUMENT_ROOT: /.../public_html
HTTP_HOST: www...co.uk
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php