Selecting multiple paragraphs with different paragraph properties normally makes these properties have undetermined state in the selection's Paragraph Properties dialog. But not for inserted page breaks.
1. Create new text document
2. Type "lorem<enter>ipsum"
3. Apply any page style (double-clicking it on Stylist) - this step adds Insert->Page break to the very first paragraph.
4. Ctrl+Home; Format->Paragraph->Text Flow tab; check that the Break setting is checked; also check Hyphenation->Automatically, and Keep with next paragraph, just for comparison; apply and close dialog.
5. Shift+Down to select the whole first paragraph, and the beginning of the second.
6. Format->Paragraph->Text Flow tab
Actual: both Hyphenation->Automatically and Keep with next paragraph are in undetermined state, showing that different paragraphs in the selection have different values for the settings; but Break checkbox is simply unset.
Expected: Break checkbox must be also in undetermined state.
Tested with Version: 126.96.36.199 (x64)
Build ID: 2ce5217b30a543f7666022df50f0562f82be0cff
CPU threads: 12; OS: Windows 10.0; UI render: GL; VCL: win;
Locale: ru-RU (ru_RU); UI-Language: en-US
and with OpenOffice.org 3.3.0 OOO330m20 (Build:9567).
I confirm it with
Version: 188.8.131.52.alpha1+ (x64)
Build ID: e92dcfdc7bd7b237e0bee26ff226a102d9e8e766
CPU threads: 4; OS: Windows 10.0; UI render: GL; VCL: win;
TinderBox: Win-x86_64@42, Branch:master, Time: 2019-05-14_00:00:57
Locale: en-US (de_DE); UI-Language: en-US