Two strange/buggy behaviours in long press popup entering negative values

[dunaek]

First: great app, love it
My environment: sony z1 compact (1280x720), android 5.1.1
I'm a programmer myself and if I had the time I would try to support this project. But in this case I'm only a User giving feedback.
(Perhaps it would be better to handle the following as two seperate issues.)

1. Popup buttons disappear when textfield gets negative.

When the popup shows I can see a textfield with a "0" in it and the configured buttons. When I press a button with a negative value the textfield shows the value, but all four buttons disappear. That happens always in that moment when the value in the textfield gets negative (e.g. press +5 once and 6 times -1). The space to the right of the textfield blanks out.

2. Android number keyboard does not show the value of the popup textfield.

When the popup shows the textfield shows a selected "0". When I click on the textfield the android number keyboard shows up fullscreen (no calculator: just buttons for digits, period, comma, minus (probably for unary reasons), space (I don't know what's that for), backspace, "GO" and its own textfield). It shows the "0", not selected and with the cursor on the left or right side depending on the touchclick I made on the popup textfield.
When I press "-" while the cursor is on the right side the "-" is not shown! But "internal" it is there because when I press OK a popuperror says "invalid calculator entry" and if I use the back button the "0-" is shown in the textfield of the popup (and the buttons disappeared (see 1). And if I press backspace the internal "-" is deleted with nothing happening in the keyboard textfield, the second backspace deletes the "0".
The Problem seems to be that the android number keyboard does not show every input. Probably if it thinks that this character does not lead to a valid number. But "0-" would be a valid term if another digit followed: "0-2". And this works: starting with "0" and cursor to the right keyboard, pressing "-2" shows "02" in the keyboard (wrong) and when I press OK the app counts "-2" (correct "0-2"). So the number keyboard accepts and shows only valid numbers but still sends the ignored characters to the popup textfield and by pressing OK the app evaluates the textfield as a term.
I tested some more values. They all lead to that conclusion.

I hope you can verify that behaviour in other environments since that wouldn't mean that the sony z1c users are alone with this problem.

[nolanlawson]

Thanks for the bug report. I'm not maintaining this app anymore, but would love if someone submitted a pull request!