Buttons disappear and Add Media stops working in Text Mode after a few minutes

For some reason, the following happens (all major plugins disabled, and tried the ‘concatenate false’ addition to wp-config; neither helped):

– I only use Text Mode when adding a post
– When adding a new post, all formatting buttons are visible (blockquote, bold, italics etc) and the Add Media button works (launches the media window etc) and they WORK
– After a few minutes (2/3/5, not sure) of writing the post, the formatting buttons disappear and the Add Media button stops working
– On all old posts, no formatting buttons are visible and the Add Media button doesn’t work (doesn’t spawn the media window etc)

PLEASE help. This has effectively reduced me to having to hurry up my posts or repost posts etc.

Thanks!