If you want to be able to use touch input while annotating, you have to go into the settings and turn on the setting to "Enable touch input in stylus mode" (this assumes stylus mode is enabled which is required for fast writing with the pen tool). Just be aware that having touch input enabled can result in accidental triggers of zooms and/or panning if you rest your hand on the screen.
As far as using touch input outside MobileSheets, if stylus mode is enabled and touch input is disabled, it's best to exit the annotation editor before switching to other applications on the device. Right now, I'm not re-enabling touch input if you switch from MobileSheets to another application while the annotation editor is active (this will be fixed in the next update). So this might explain why you are seeing that. As a side note, on the main Onyx status bar, you can toggle touch input detection on/off at the top right, which would fix this issue as well. Their status bar will show that touch input is enabled even if MobileSheets disabled it, because they must not be monitoring if an application has changed the state of that toggle. So even though it appears like touch detection is enabled, toggle it off then back on to fix this (this won't be required after the next update is released though, and it's also not required if you exit the annotation mode in MobileSheets before switching out of the application).
Mike
As far as using touch input outside MobileSheets, if stylus mode is enabled and touch input is disabled, it's best to exit the annotation editor before switching to other applications on the device. Right now, I'm not re-enabling touch input if you switch from MobileSheets to another application while the annotation editor is active (this will be fixed in the next update). So this might explain why you are seeing that. As a side note, on the main Onyx status bar, you can toggle touch input detection on/off at the top right, which would fix this issue as well. Their status bar will show that touch input is enabled even if MobileSheets disabled it, because they must not be monitoring if an application has changed the state of that toggle. So even though it appears like touch detection is enabled, toggle it off then back on to fix this (this won't be required after the next update is released though, and it's also not required if you exit the annotation mode in MobileSheets before switching out of the application).
Mike