Created attachment 116930 [details]
missing appmenu in title bar

SUMMARY
As in subject. Please check attached screenshot.
Used Widget Style is Oxygen.
In first run of Dolphin appmenu button is placed correctly, only after couple of restoration of session (relogin, restart system) just disappears. This is annoying, because I don't have access to main menu.
Please note that restoring of this button menu is correctly done in KDevelop.

Additionally please note that in directory ~/.config/session in case of every closing of Plasma session are creating new files like for instance:
dolphin_1011d10dde79000153410977300000006860022_1544823224_495836
It is noteworthy that in case of KDevelop in mentioned directory is always placed only one file.
Below please find list of names of files after several of relogin to Plasma.

-rw------- 1 piotr piotr 1156 12-10 21:51 dolphin_1011d10dde79000153410977300000006860022_1544475089_161169
-rw------- 1 piotr piotr 1156 12-11 18:16 dolphin_1011d10dde79000153410977300000006860022_1544548570_778075
-rw------- 1 piotr piotr 1156 12-12 18:13 dolphin_1011d10dde79000153410977300000006860022_1544634801_371128
-rw------- 1 piotr piotr 1156 12-13 18:14 dolphin_1011d10dde79000153410977300000006860022_1544721293_442101
-rw------- 1 piotr piotr 1156 12-13 22:22 dolphin_1011d10dde79000153410977300000006860022_1544736147_936161
-rw------- 1 piotr piotr 1156 12-14 18:53 dolphin_1011d10dde79000153410977300000006860022_1544810008_328774
-rw------- 1 piotr piotr 1156 12-14 21:03 dolphin_1011d10dde79000153410977300000006860022_1544817819_434772
-rw------- 1 piotr piotr 1308 12-14 22:32 dolphin_1011d10dde79000153410977300000006860022_1544823173_900082
-rw------- 1 piotr piotr 1156 12-14 22:33 dolphin_1011d10dde79000153410977300000006860022_1544823224_495836


STEPS TO REPRODUCE
0. Set restore session of Plasma
1. Set "Widget Style" (in Application Style) as Oxygen
2. Set appmenu ("Application Menu") in Application Style -> Window Decorations -> Buttons
3. Run Dolphin
4. Log off, log in couple times to Plasma

OBSERVED RESULT
appmenu ("Application Menu") just disappears in one of next restored Plasma session. Another effect might be that main menu looks like normal (options placed in bar).

EXPECTED RESULT
appmenu ("Application Menu") should be always placed in left top corner (in place where user set it) and looks like (usually hamburger) button.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: YES
(available in About System)
KDE Plasma Version: 5.14.4
KDE Frameworks Version: 5.53
Qt Version: 5.12

ADDITIONAL INFORMATION