If a file is opened by following a link in a text region (as frequently used in multipage interactive handbooks), then the history function is broken. Whatever edits you do, the undo button doesn't become green and Ctrl-Z doesn't work.
Also, the change indicator * does not appear in the title bar.
It is, however, possible to save the changes.
If you open the same files via File> Open, then the history works as expected.
(applies for portable and non-portable version)
SMath Studio: SMath Studio Desktop 0.98.6179.21440, portable, x64
OS: Microsoft Windows NT 6.1.7601 Service Pack 1 (Microsoft Windows 7 Professional , x64)
Screen: 1360x768 px, 96x96 dpi
Localization: separator=<semicolon>; decimal symbol=<comma>; system decimal symbol=<comma>; language=GER
Frameworks: CLR 2.0.50727.5485
installed versions:
v2.0.50727 2.0.50727.5420 SP2
v3.0 3.0.30729.5420 SP2
v3.5 3.5.30729.5420 SP1
v4
Client 4.6.01055
Full 4.6.01055
v4.0
Client 4.0.0.0