I've been using visio 2013 for a couple of weeks, no problem with automation and always with .vsdm files. But today, I kept loosing the developer tab from .vsdm files, despite careful saving.
In the end I realised that authored file content and/or modules of any kind were not relevant to the problem.
I made two files,
A. a Visio 2010 .VSD file with Developer tab visible. However many times they were opened or closed, the developer tab always showed. File= Kelvin4TestVisio-2010.vsd
B. a Visio 2013 .VSDM file with Developer tab open when loaded to the EE site. When the file was re-opened for the first time, the developer tab was present, but repeat the reopening again ... and the tab disappears. So I checked Options>Developer tab display and saved file again: but the same occurred: two re-opens and the tab goes invisible! There was no author-written vba code in this file. The file remained a .VSDM file; it never turned itself into .VSDX.
I could not load file B; .VSDM files are not yet accepted by my EE site.
Sadly, experience says 'user error' ... but how so, after so many happy hours of normal service?
Incidentally, can VBA be written in the document module to instruct the developer tab to be visible when the visio file first opens?