Describe the bug
When manually setting a column width, and then setting another column width, the first column width changes and doesn't keep the value already set.

To reproduce
Steps to reproduce the behavior:

1. Add a Columns block with 3 columns.
2. Manually set the first column width to 5.
3. Skip to the 3rd column and manually set that column to5.
4. Observe that the first column grew in width by itself and didn't keep the manually set value.

Expected behavior
I expect the columns to keep whatever manual width I set.

Screenshots

Desktop (please complete the following information):

• OSX Catalina
• Chrome 78.0.3
• Gutenberg 7.1